Fuel/N₂ and fuel/air mixtures were treated with non-thermal DBD plasma and the changes in characteristics of laminar diffusion flame have been observed. Flame of fuel/N₂ mixture generated more soot under plasma condition while less amount of soot was formed from fuel/air mixture flame. Luminescence spectrum and gas chromatography results confirmed that plasma energy converts a fraction of fuel molecules into radicals, which then form C₂, C₃, C₄ and higher hydrocarbon under no oxygen condition or turn into CO, CO₂ and H₂O when oxygen is present.